95 % efficiency SMPS

[ronsimpson]

This thread started out about 95% PWM. I believe 95% or 90% or ever 85% is not the real problem.
If you short out a solar panels you get 0 volts and maximum current.
0 voltage X max current = 0 watts
If the current is 0 then the voltage is maximum.
Max Voltage X 0 current = 0 watts
There is a sweet spot where watts = maximum and voltage = ? and current = ?
Solar power supplies I have designed are constantly looking for the sweet spot. If a cloud or maybe a bird goes overhead the duty cycle changes to get maximum power out.
I know “%” is important. If you don’t know how to get the most out of you panel under all conditions you are likely not using 30% to 50% of the available power.

 

[Thunderchild]

ron I understand what you are saying but that is not quite what I am asking, you are talking full blown MPPT I'm just talking a SMPS with high efficiency, wheather I use it on my panels or not is another matter. as it happens I've ordered a charge controller (not of the MPPT type), I would assume that the panels best general sweet spot is around the nominal voltage output, give its just a 40 W setup I'm not in too much of a hurry for MPPT.

as far as MPPT is concerned at the end of the day you want to charge the battery as best you can by providing say 12.5 volts when the battery is at 12 and 13.5 when it reaches 13 v what the panel puts out it puts out and a SMPS (the heart of a MPPT) will just take whats available and match it to the load, I don't understand how the controller can match itself to the solar panel surely it will take what it is given.

see at the moment I have a battery at 12.5 volts, now if I directly connect the solar panels it shoots up to 16 volts, the panel is outputting I beleive 17.5 ish, now if I had a proper circuit on there it would take that 16-17.5 volts and step it down (with 90+ % efficiency) to 13 volts the 4.5 volta difference being converted to extra amperage

17.5 V X 1.15 A = 20.125 W X 0.9 = 18.1125 = 1.393 A a gain of 0.243 A

0.243 / 1.15 X 100 = 21 % increase in current output !!!

now it goes without saying that at 80 % (what i have now) I'm just keeping the voltage under control to stop my battery boiling to bits at 16 volts, I might as well use a 1.5 R resistor as all that is gained is lost in the conversion, but with 90-95 % as you can see from above I start to make gains, erm what was all that fancy theory about MPPT's ? isn't just what I explained ? ok a MPPT will increase the output as the battety charges and at fully charge the gain is less but the battery is kept under control.

 

[Thunderchild]

of course back to the original thread, I am still interested in the factors that govern any SMPS efficiency,

for example, I now have 12-14 volts on my hands, now whats the point in turning 12 volts into 240 with an inverter loosing 10 % in the inverter (oh yea a full blown inverter is 90 % efficient so how come a simple SMPS with less stuff can't be 95 % ?) I then plug into my inverter the wall wart for my router which will reconvert 240 V to 12 again with 90 % efficincy again so I end up with 12 V anyway but I've just dumped 20 % of the power... now why not just use the 12 V direct with a SMPS, of course if its 80 % efficient anyhow I'm wating my time, ok I can't convert 12-14 V to 12 V with a SMPS but speakers working at 9 V ? or if I was to have a 24 V system...

 

[smanches]

One of the caveats of using a lower frequency is the circuit can't react to changes in input or output as quickly. And you get much more ripple.

This isn't that important in solar charging systems though.

 

[Thunderchild]

One of the caveats of using a lower frequency is the circuit can't react to changes in input or output as quickly. And you get much more ripple.

This isn't that important in solar charging systems though.

quite which is why I'd be quite happy to go low for charging, I do have a datasheet of a small 1 A SMPS chip that is 95 % efficient so what all the fuss about it being almost impossible is I don't know. I think the motto of this forum should be "No you CAN'T !!!!!!!! (because we can't be arsed to admit we wouldn't bother ourselves)"

 

[Nigel Goodwin]

quite which is why I'd be quite happy to go low for charging, I do have a datasheet of a small 1 A SMPS chip that is 95 % efficient so what all the fuss about it being almost impossible is I don't know. I think the motto of this forum should be "No you CAN'T !!!!!!!! (because we can't be arsed to admit we wouldn't bother ourselves)"

If you think it's so easy, then go ahead and do it - but I suspect you'll find it VERY, VERY difficult to approach 95% efficiency - even using the chip you mention above.

For a start why not build a simple one and experiment with frequencies etc. to find what affects efficiency the most?.

 

[Thunderchild]

For a start why not build a simple one and experiment with frequencies etc. to find what affects efficiency the most?.

after people having oposite opinions on what is more efficient it seems the best thing to do

 

[Nigel Goodwin]

after people having oposite opinions on what is more efficient it seems the best thing to do

I would suspect it's because there's no single fixed thing that affects efficiency, it's a question of the overall design - people finding lower the frequency helps just happen to have a circuit which benefits from that.

 

[Thunderchild]

well we've had oposing opinions on what dutycycle does and why there must be some factual information rather than rumors

 

[smanches]

17.5 V X 1.15 A = 20.125 W X 0.9 = 18.1125 = 1.393 A a gain of 0.243 A

0.243 / 1.15 X 100 = 21 % increase in current output !!!

what was all that fancy theory about MPPT's

The problem is that solar cells have fixed POWER output and act more like a constant current source. You can't just expect max voltage to be max power and drop it accordingly.

As Ron was saying. Max voltage = zero current. Max current = zero voltage. Both = zero power. So someplace in between those two extremes is the max power point.

On another thread, a poster mentioned not tracking the input voltage and current, but just track the output current. Max output current = max power since output voltage is basically fixed.

**broken link removed**

EDIT: I guess my point is, a standard buck regulator increases duty cycle to increase power output. This does not work with solar. The duty cycle is going to be directly related to the power curve on that graph. They call it a Tracking controller because it's not just adjusting in one direction, but testing both sides of the current duty cycle to see if decreasing or increasing it is going to give more power.

 

[tcmtech]

I thought this site made it rather simple as to what you are actually looking at for finding the actual peak efficiency point of a solar panel.
Measuring the Power of A Solar Panel - Solar



As I have understood it a solar panel is designed to work with a specific voltage in mind is typically "tuned" to work with its peak efficiency range around the actual working range of the battery system its designed to be connected to.

And a charge controller just dumps that excess energy when that battery being charged get to its full voltage.

I do not see what the big fuss is all about? If your using a solar panel array designed for a 12 volt system then it will have its peak efficiency in that 12- 15 volt range the battery normally works at.

Its actual output voltage can go way higher but the amps you can pull off it are small and the total power available at the voltage is actually less than if you load it up and pull it down to the peak operating range.

If your battery is going bad or if your solar panels are over sized then you will be getting too much voltage rise in your battery. And that is the whole point of the load dumping charge controllers. To load the system only at voltages higher than the battery should run at.

Yes, they appear to be wasting power by dumping it as heat but its free power you cant use anyway unless you have an actual load on the system that is equal to the power coming in.
If your battery is too small you cant store all of the extra power your panels are making regardless of what type of voltage conversion setup you are trying to use reguardless of its actual efficiency!

You either need to have a load on the system doing something usefull for you in order to use that energy beneficially or you just have to dump it!

 

[smanches]

As I have understood it a solar panel is designed to work with a specific voltage in mind is typically "tuned" to work with its peak efficiency range around the actual working range of the battery system its designed to be connected to.

And a charge controller just dumps that excess energy when that battery being charged get to its full voltage.

Solar panels are designed to purposely put out more voltage than is typically required by any application. This is to make up for voltage drop on cloudy days so you still have enough voltage to work with. There is no tuned voltage, other than the MPP, of which the curve changes depending on sun output.

Solar charge controllers don't dump energy, they just don't use it. I'd like to see ones that do, so I might understand why they would do it. It doesn't make sense by any means.

 

[tcmtech]

I am just starting to learn more about solar panels. And I am coming to different conclusions based on different information sources.

So most charge controllers simply disconnect the panel from the batteries when they reach a specific voltage?
They dont just add variable load to them to keep the panel loaded down to a specific voltage?

I do understand the need for the higher voltage output of a solar panel but however, I have always understood it that there was always a sweet spot that was the panels peak output point. And Like that web site I referenced, that sweet spot happens at a lower voltage and current that what you can get out of the panel during open circuit or short circuit conditions.

If a cloud goes by the higher output voltage available keeps the panels output high enough to still provide a charge for the battery but the amps will go down due to less total power being put in.

 

[Thunderchild]

surely the controller will just use what power it gets providing the input voltage is Vout+2 the desired output voltage is guaranteed and what current is provided will be made use of, if the panels voltage goes high well the regulator is efficiently reducing that voltage to the desired output voltage and increasing the current output accordingly, really what more can you do ? would it be any different for a wind turbine ? I don't here of fancy controllers for wind turbines but oh... they are not so popular are they.

it is of course obvious that if your going to output 14.4 volts and the battery is dead at 11.5 volts your going to throw away almost 3 volts which multiplied by the amperage supplied gives you the total watts of usable power being wasted. so if your regulator starts at 12 V and rises gradually by say 0.5 V more than the battery voltage (sampled by occasionally disconecting the supply and probing the battery voltage after say 30 seconds) then you will make better use of the available power, you can't change what the solar panel is giving you can you ? but you can adapt the changing load as best as possible.

 

[Thunderchild]

If a cloud goes by the higher output voltage available keeps the panels output high enough to still provide a charge for the battery but the amps will go down due to less total power being put in.

and in that case the SMPS will automatically reduce duty cycle to take into account the increased input voltage and so output more current than if the panel was directly connected to the battery. as there is less amps available in such a case you could decrease the output voltage slightly as the battery will require less of an "over voltage" to charge the smaller current giving you a small (negliable possibly) increase in efficiency under cloudy conditions, erm we are still talkiong about the standard abilities of a SMPS aren't we, so what all the special stuff ? where is it ?

 

[tcmtech]

Dont know myself!

I do understand that wind and solar both have their regions of application. If you live where its cloudier but have loads of wind like I do, wind based power generation is super.
But if your in an area with low winds or a urban environment you cant put up a wind generator or get much out of it. Thats where the solar panels have a solid advantage!
Plus there are far different operating characteristics in a wind based system Vs a solar panel system. Solar panels can be disconnected from a load and have nothing happen.
While a wind generator could possibly spin itself to pieces!
Solar only works most efficiently during sunny days. Wind power can work 24 hours a day.

There are also trade offs in the designs too! Solar panel based power systems are fairly expensive even when you build them yourself. Wind power is capable of much higher power per square unit of measure. And the system can easily be made from simple components and still work with fair average efficiency.

I am not 100% all wind or all solar! I know they both have areas of advantage and disadvantage.

As far as control systems go, wind has just as many control systems available as solar! However wind power generally uses some form of shunt voltage regulation.
Wind controllers dump the excess power away from the batteries in order to keep the load on the generator. Thats where I assumed solar did it the same but apparently it does not!

I played around and experimented with battery based power storage for years. I got sick of all of the battery maintenance and the need for the charge control and what not! Plus only having what was stored in the batteries available for power. And when there was more power available than what the batteries could hold I could not do anything with it but make wasted heat!
On top of all of that the having to run anything that required 120 volts AC power needed to have an inverter of some sort and was still limited to what that inverter could put out!
Well you know that part!

It was my actual searching for a bigger better inverter and storage system that lead to my doing the research and development work on grid tying the power generation sources to my utility power.

Once I got the grid tie bugs figured out, the charge control system, batteries, and inverters got the boot and I never looked back with any serious intentions!

You know any one that wants to buy ten 6 volt 200 Ah Exide industrial storage batteries? $25 each you haul them! 8 are still in great shape! two have cracked cells at one end. The wood cabinet is included!
they will be cleaned up and tested before pickup and I will load them too!
(The salvage dealers will pay $25 each too so they wont get any cheaper.)

I am just simply trying to understand a form of alternative power that I currently do not have much applied knowledge in. Nothing more!

 

[Funny NYPD]

95% is a very high target, and every single components must be selected carefully.
90% might be a more achievable goal without using fancy components.

 

[ronsimpson]

**broken link removed**

 

[Thunderchild]

if the solar panel works best at its nominal voltage then the charge current could be controled which would in turn control the panel load to make it so that the input stays at 17.5 volts in the case of my panels but I still don't understand how you expect to improve the panels output in the case of cloud. My panels drop the output current to 10 % when its cloudy

 

[dougy83]

These guys reckon they've made a 98% eff MPPT: **broken link removed**

There are a bunch of SMPS controller ICs available, efficiencies are approaching 95% under certain conditions. There are some simple ways to markedly improve on some of these efficiencies through some simple (and some not so simple) methods - e.g. use of a schottky in parallel with the free-wheeling FET may increase the eff by 2% (ref: 2nd link below). Use of Litz wire may reduce skin-effect losses in the inductor. Switching at troughs(/peaks?) of the output may also improve efficiency if done correctly.

I would assume that the use of lower frequency does not necessarily make for better efficiency. Higher frequencies (within reason) allow use of smaller value components that may allow lower ESR type capacitors to be used.

Some ICs I saw were: https://www.electro-tech-online.com/custompdfs/2009/04/LM5116.pdf, TPS40050/1/3 https://www.electro-tech-online.com/custompdfs/2009/04/14410.pdf

Regulation feedback will of course be from the input, to keep it at a stable 17.5V (or whatever the optimum voltage is). The output voltage will be automatically regulated by the load (e.g. battery or motor), although over-voltage protection may be desirable in e.g. battery charging.